Shaft-positioning servomotor mechanism



June 7, 1960 .1. VERHOEFF 2,940,031

SHAFT-POSITIONING SERVOMOTOR MECHANISM Filed NOV. 1. 1956 INVENTOR JACOB VER HO EFF E'M j AGEN United States atent O 2,940,031 SHAFT-POSITIONING SERVOMOTOR MECHANISM Jacob Verhoelf, Hilversum, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware This invention relates to a shaft-positioning mechanism for positioning a rotary shaft 'in a plurality of predetermined positions and has for its-object to provide a shaftpositioning mechanism of. thisi'kind which has a higher accuracy-and a high speed of positioning. The high accuracy of positioning with the shaft-positioning mechanism according to the invention may be achieved without a large number of very accurately processed parts being required. The'said shaft-positioning mechanism is characterized inthat it comprises two rotary adjusting members, of which the first adjusting member during the adjustment always determines the end of a sector of the total angle of rotation which this adjusting member can perform, within which sector the ultimately desired position of this shaft is situated and the second adjusting member inthe opposite direction of rotation determines the ultimately desired position of the shaft within the sector, determined by the first adjusting member and starting from the end of the sector determined by the first adjusting member, provision being made of a driving shaft which simultaneously drives the two adjusting members with the interposition of the transmission mechanism between the shaft and the first adjusting member having a retardation greater than that of the transmission mechanism between the shaft and the second adjusting member. g

In a further embodiment of the invention, all sectors have the same angular value and are whole parts of 360, the ratio between the speeds of the adjusting members per unit-time being equal to the number of the sectors. Consequently, a uniform division of the positions to be adjusted through 360 may be obtained.

In another embodiment of 'the invention, the shaftpositioning mechanism is preferably driven electrically, the first adjusting member, hereinafter referred to as the sector-adjusting member, comprising a collector which is so connected to the circuit that, when the chosen sector is reached, the direction of rotation of the driving shaft reverses, a coupling provided between the sector-adjusting member and the collector permitting free movement of the sector-adjusting member with respect to the collector. In this embodiment of the invention, it is thus possible to choose the desired position of the shaft at any arbitrary distance from the shaft proper.

In another embodiment of the invention, if all seetors have the same value, the free movement of the sector-adjusting member with respect to the collector is effected through an angle having the same value or a higher value than the angular value of the sectors.

The second adjusting member which determines the ultimate position of the shaft, is constituted in another embodiment of the invention by two parts, of which one part. comprises a ratchet wheel and a collector which is rigidly connected therewith and the other part is an auxiliarymember driven by the: driving shaft, a coupling pro- .vided between said parts allowing of free rotation of the auxiliary member with respect to the ratchet wheel in one direction of rotation, while in the other direction of 'to the ratchet wheel.

2 rotation the auxiliary member can. perform a rotation of at most 360 with respect to the ratchet wheel. Consequently, the possible rotation of the sector-adjusting member is determined by the relative positions of the auxiliary member and the ratchet wheel.

In another embodiment of the invention, an electrically operated pawl is provided which can co-operate with the ratchet wheel, the position of the pawl being determined by the position of the collector which is rigidly connected As soon as the collector has reached a position determined by a selecting collector, the pawl meshes with the ratchet wheel and locks it.

In a further embodiment of the invention, it is possible for the auxiliary member and the ratchet wheel to be arranged on a common shaft so as to be rotatable about thisshaft, a friction coupling being provided between the said two parts. However, in another preferred embodiment of the invention, the ratchet wheel-together with its collector is driven by a separate shaft, preferably .with the interposition of a retarding gear. This embodiment affords advantages, particularly in connection with the desired short time in which the shaft should be adjusted which requires a high speed of the auxiliary member, since in this embodiment of the invention the release time of the relay which controls the pawl is much less important.

7 In one embodiment of the invention, the shaft to be positioned may be driven by the sector-adjusting member. In this case positions can be adjusted only which are located within an angle of 360. This suffices in most cases for example, fortuning capacitors, resistors and similar parts. However, if it is desired to adjust also tappings on inductances and similar parts, in which event angles of several times 360 are traversed by the shaft to be positioned, this shaft, in another embodiment of the invention, is coupled directly with the driving shaft.

In order that the invention may be readily carried into effect, it will now be described, by way of example, with reference to the accompanying drawing showing diagrammatically in Fig. 1 the electrical and mechanical structure of a'shaft-positioning mechanism.

Fig. 2 is an enlarged diagrammatic showing of the connection between the worm wheel 2 and collector 4.

A shaft 1 tobe' positioned carries a worm wheel 2 which is rigidly connected thereto. The worm wheel 2 carries a pin 3. Rotatably arranged on the shaft 1 is a collector 4 which comprises a conductive ring which contains a small sectors having an angular value of less than 10 and which is of non-conductive material. In total are 36 fixed sliding contacts 6 arranged with equal spacings on the periphery of the collector 4. The collector also has a groove .7 in which the pin 3 engagesand which occupies an angle of a little more than 10. This additional value isrequiredin view of the thickness of pin 3. This implies that the Worm wheel 2 can cover an angle of 10 in each direction of rotation without the collector 4 being taken along. The worm wheel 2 is driven without backlash by means of a worm 8. Furthermore, a sliding contact 9 is provided which is rigidly arranged and connected to the inner side of collector 4.

The worm 8 is rigidly connected to a driving shaft 10, whichcarries a screw wheel 11. The screw wheel 11 drives an auxiliary member 12 which also has the form of a screw wheel and which can rotate freely about a shaft 13. The transmission ratio in this embodiment between the worm 8 and the worm wheel 2 is 1:36, whereas for the screw wheel 11 and the auxiliary member 12 this ratio is 1:1. The auxiliary member 12 has a pin 14. A ratchet wheel 15, which in this case has 50 notches 16, can likewise rotate freely about the shaft 13, said notches being-uniformly divided over the circumference of the ratchet wheel 15. A simple friction coupling 12a is provided betw'eenthe auxiliary member 12 and the ratchet wheel 15. The ratchet wheel .15 furthermore .has..two

pins 17 and 18 which are rigidly secured thereto. A

pawl 19. can rotate about 1pm 17, which pawl has a. V

'- shaped entremity 2i} and is,normally pushed against '38 by means of a springs; secured to I'a lpin 22 at tor 22 of conductivema'terial, in which 23 of non-conductive material is placed. ,On the outer side of this collector are provided 50 sliding contacts which are rigidly arranged and "divided l niforrnly ,ovjer 3-60", .while motor now starts to rotate in such manner that both the -sector-adjusting member 22-and the auxiliarymember 12 a sliding contact 25, 'l'ikewise'rigidlya in co ntact with the inner side 'of the r.

*A pawl 26 meshes withthe .ge of' ratchet wheel int 127. The-position i5 and can rotate about a fixed of the pawl is determinedbyh stationary relay 28, the

pawl itself co-operating with an electric contact 29, so that this contact is open when the pawl meshes with. the

drivenby an electric motor 31,

ratchet wheel 15 andisiclosed whenithe pawl is attracted pling 30 is ofiknown type whichswitclies off when the shaft 10 is loaded above a predetermined value and which automatically switches on again when the overload on the shaft 'is eliminated. When the connection 'between the electric motor 3'1 and'the shaft'10 is interrupted, the overload coupling operates in khown manner a switch 32. In'the case shown, the switch 32 is interrupted when overload occurs and the contact'in the switch is restored again when the overload is "eliminated. The

switch used may be, for example, of the micro-type. Fur-' thermore, a reversing relay 33 is provided which determines the direction'of rotation of the electric'rnotor 31.

mine the positions or the collectors 4 and 22. The selectingcollector 34has a conductive portion 35 having a conductive sector 36; while the portion 37 is insulating. On its periphery there are provided '36 sliding contacts 33 which are fixed and regularly divided over 360, one

'fixed sliding contact 39 being provided on its inner side.

The selecting'colle'ctorfitl likewise 'has'a conductive inner ring 41 with a conductive sector i2 and an insulating outer ring 43 and comprises "fi'x ed sliding contacts &4,

which are arranged, likewise regularly'divided over 360,

on the outer'side of the collectoh one fixed siiding contact 45 being in contactwithtthe' inner. sideof the collector.

Now, the operation of the shaft-positioning mechanism 7 described will be explained hereinafter, it'b'e'in'g assumed I that a direct-current source is connected to the device, that is to say to the plus terminal atyio and to .the minus "terminal at 47! Let it be assurned'that a new position of the shaft 1 is desired, so that both the collector 34 and the collector it) must be rotated; thecorrect positions of these collectors, corresponding to this new position,

may be read for example one chart. When these posii tions have been reached, then primarily a circuit extending from 46 through sliding contact 39, sector 35, sliding contact 38, sliding contact (i collector 4, sliding contact 9, reversing relay 33 to 47 is completed. Consequently,

the armature of reversing relay 33 is attracted and the contacts 48, 49- and 5t 51 are closed; At the same time, a circuit extending from 46 through "sliding contact 45, collector 40, sector $2., sliding contact 44, sliding contact 24, collect'or'ZZ, sliding contact 2Y5, r e1ay2 8 to the minus terminal 47 has been established. Consequently, the. relay 'Two selector means being collectors 34 and 40 dete'rrotate in the counter-clockwise direction. This is possible, since the shaft 10 and the electric motor 31 are coupled together by the coupling 30. The contact in the switch 32 has also been restored in 'themcantime.

The ratchetwheel -;1-5 and ithe collector 22 are initially driven by the friction coupling 1211. However, the collector need perform at most only one revolution (expressed exactly: -360-about 8') since each new position which corresponds to the position adjusted by collector 40-is-then certainly reached. "When the collector has reached the new position, the relay 28 is no longer energized (circuit 46-45-41-427-44-24+23e22-2528-47 is interrupted) and the pawl 26 is released and engages the ratchet wheel 15; furthermore, the switch 29 is opened However, collector .4 usually has not reached then the new position corresponding tothe new position of collector 34 but the auxiliary member, after the pawl 26 has engaged the ratchet wheel, can continue its rotation in the same direction, since on the one hand the reversing relay 33 is still energized and onv the other hand the pin 14 can always rotate in the counter-clockwise direction, since the pawl 19 canbe lifted. The auxiliary member '12 rotates 36. times as rapidly as the sector-ad justing member 2.. i When the sector-adjusting member 2 with its collector 4' has also reached the position in which the collector position corresponds to the position of collector ,34, the reversing relay becomes deeenergized (now circuit 46 39,+35,-36-138-6.5- 9-.-3347 is in errup and thedirection of rotation of the electricmotor 31 reverses; This motor in itself nowreceives current through the switch 32 which is still closed. Now, the auxiliary member 12 also rotates in the clockwise direction till the pin 14 abut against the V'-shaped extremity of the pawl 19. The auxiliary member then cannot rotate further and overload on the shaft 10 occurs and the overload coupling 30 becomes operative, with the result that the contact 32 is opened and the electric motor comes to a standstill. During the rotation of the auxiliary member 12 in the clocltwise direction, the sector-adjusting member 2. has also rotated in the clockwise direction so that the shaft 1 to be adjusted also rotated in the clockwise direction.- However, the collector 4 remains a re t due to t e p y of pin 3 n he g o e In the embodiment shown, the Gollctort has 36 pofi l Qq i. h t e-tor 5 o i c cto thus may have at most an angularvalue which secures that contact is never within an angular displacement of 10 of the adjusting ii ember- 2, so that intotal 36 -50;180Qtpreset PQSitions of the shaft 1 are possible.

a When the shaft 10 passes from a determined position to a new desired position, the initial direction of rotation is always in the same direction and such that the wheel 2 ta es il; the t rl ckw s irect on. However, collector 4 starts to rotate only when the pin 3 ha abuts ted against the extremity of groove; 7-. Whenthe. correct position of'collector 4 has been reached, the movement of the member 2 reverses and pin 3, moves awayfrom the. end of groove 7, but the, collector 4, remains at rest. Due. to, the first-termtioned movement, the end of-v asector of (in this case) 10f is thus, chosen, within which the desired positionof the shaft; is. situated. As soon this and has, been reached and the pin 3 thusfhas. moved the collector. into, its. correct position and hence the shaft to bev adjusted into itsprovisional position, the. pin. 3

moves away from the end of groove 7 (that is to say the end of the sector) and the shaft 1 is moved into its definite position. From thisit follows that the angular value of the groove 7 must not be less than 10; however, it is allowed to be larger, since the upper boundary of the groove is immaterial, ,due to pin 3 never being able to engage this upper boundary. Consequently, the member 2 is actually a sector-adjusting member which primarily determines the end of a secto It is by no means necessary for the collectors 34 and 41 to be adjusted simultaneously. When collector 34 is adjusted first, the motor already starts to rotate, but this is not objectionable, since the auxiliary member 12 can keep rotating in the counter-clockwise direction, even when the ratchet wheel 15 is still arrested by the pawl 26. The pin 14, rotating in counter-clockwise direction, then lifts the pawl 19 against the pressure of spring 21 and can continue'its rotation. The pawl 26 releases the ratchet wheel 15 only after the collector 40 has also been adjusted and now the ratchet wheel 15 follows the movement of the auxiliary member 12.

In the foregoing it has been assumed that both collectors are rotated, simultaneously or not simultaneously. It is possible, however, that purposely only the collector 34 is adjusted. This case occurs, for example, when the position of shaft 1 must ebevso varied that a whole number of times 10 must be added to the position or subtracted therefrom. In this case, the position of collector 40 does not vary and the pawl 26 keeps in engagement with the ratchet wheel 15; the sector-adjusting member 2 then rotates in the counter-clockwise direction, dill the end of the new section has been reached, the pin .14 continuing its rotation under the pawl 19. When this end has been reached, the movement reverses and :as soon as pin 14 has engaged the pawl 19, the new position is reached, which thus differs n times 10 from the :pr evious position.

0n the other hand, it is also possible that a new position is desired which differs only by a small angle, for example 3, from the previous position, the new position being situated within the sector, within which the previous position was located and hence, for example, when passing from 93 to 96. In this case, only collector 40 is rotated and collector 34 remains at rest. During the :rotation of collector 40, the pawl 26 is then immediately lifted and since the relay 33 receives current through contact 29, the motor again rotates in the counter-clockwise direction until collector 22 again has a corresponding position.

-In the meantime, the sector-adjusting member 2 has also been driven, but since the desired adjustment of the shaft differs by less than 10 from the previous adjustment, the rotation of the member 2 is now so small that'pin 3 cannot engage the end of groove 7 before the reversing relay is already de-energized due to the meshing of pawl 26. The collector 4 thus remains at rest and, after the direction of rotation has reversed, the pin 3 again moves back, but a little farther than the previous position was. As before, the special position of pin 14 with respect to ratchet 19 at the moment of the reversal of the movement determines the extent of the backward movement of pin 3 and hence the ultimate position of shaft 1.

Finally, it is possible that the shaft, instead of being moved from 93 to 96 must be moved from 96 to 93", in which event, for example collector 40 is rotated a small amount in the clockwise direction. The collector 22 must then be rotated by almost 360, but in the majority of cases the pin 3 then has already engaged the end of groove 7, so that collector 4 starts to rotate. As soon as this happens, the first circuit is also closed and although the pawl 26 has already meshed after a rotation of collector 22 of almost 360, the sector-adjusting member 2 and the auxiliary member 12 continue to rotate until the first 360 have been covered. At this moment, however, the reversing relay is definitely de-energized and now the correct point of adjustment may be found in the reverse direction of rotation in the manner previously described.

It has been mentioned before and has become even clearer from the foregoing that the definite position of the shaft 1 is ultimately determined by the spacial positions occupied by the pin 14 and the pawl 19 when the direction of rotation reverses. In the first place, the two parts always meet with a direction of rotation of the auxiliary member 12 in the clockwise direction, so that any backlash is always eliminated in the same direction, while the directional force, to which the shaft 10 remains subject after the coupling 30 has been interrupted,

ensures that such backlash is always eliminated with the same force. Since the unavoidable inaccuracy of the readjustment is transferred with reduction to the ratchet wheel 15, it is also clear that this inaccuracy may be much smaller than in conventional constructions. In practice, an inaccuracy of readjustment of 002 may be achieved. It is also clear that the ratio between the speeds per unit-time of the sector-adjusting member 2 and the auxiliary member 12 is solely determined by the number of sectors which the member 2 must be able to choose since after a complete revolution of the auxiliary member 12 the member 2 must have rotated by an angle such that a new sector has been chosen. The transmission ratio between the worm 8 and the sectoradjusting member 2 is thus equal to 36 when the transmission ratio between the screw wheel 11 and the auxiliary member 12 is equal to 1, since there are 36 sliding contacts; the angular value of groove 7 is at least 10, since each sector is 10 and the angular value of the insulating part 5 on the collector must be smaller than 10 for the same reason.

In view of the small time of adjustment which in certain cases is desired and the speed at which the auxiliary member 12 and the ratchet wheel 15 rotate, it may be desirable in view of the release time of relay 28, that the ratchet wheel 15 rotates more slowly than the auxiliary member 12. This is possible if it is taken into consideration that the spacial positions 'of the pawl 19 and the pin 14 with respect to one another determine the position of the shaft, as previously mentioned. It is thus fundamentally possible, and in certain cases desirable in practice that the ratchet wheel 15 is driven by a retarding gear,'and if necessary by a separate electric motor. It is in certain cases even simpler to arrange the ratchet wheel 15 on the shaft 1 freely rotatable, and to provide a light friction coupling between the sector adjusting member 2 and the ratchet Wheel 15, it then naturally being necessary that the pin 14 can continue to co-operate with the pawl 19.

Finally, it has been assumed in the foregoing that the shaft 1 is the shaft to be positioned and that this shaft can be positioned in 1800 positions only through an angle of 360. However, in certain cases it is desirable that the shaft to be adjusted should be capable of rotating a plurality of times 360. Such is the case, for example, with a shaft carrying a sliding contact which constitutes tappings of an inductance coil. Such a shaft may then be rigidly connected to the driving shaft 10, so that adjustments through at most 36X 360 are possible.

It is finally also possible for the 50 positions determined by the teeth of the ratchet wheel 15 to be distributed irregularly over 360. In this case, the difference between the possible positions, instead of being n times 0.2, is equal to another amount which is not a multiple of 02. It must then be considered, however, that this irregularity is repeated in every 10, that is to say in each sector of the shaft to be adjusted. This is not objectionable for certain purposes. Furthermore, one is not limited by sectors of 10, but other values may be chosen as well. It is even possible to utilize sectors of relatively different values. In this case, the transmission mechanisms between the driving shaft and the adjusting member ma b variable for each revolution, for exam- 7 pie by means of elliptical gear wheel orsimilar members.

The shaft-positioning mechanism'as' described is suitable not only for wireless telecommunication devices, but also for use as a dividing device for machine tools and similar machines, where accurate and rapid adjustment of the work-piece to be ,processedfor of the tools is desired.

What is claimed is:

l. A shaft positioning mechanism for positioning a shaft in a plurality of preset positions comprising first and second rotary adjusting members, said first adjusting member being rigidly connected to said shaft to be positioned, a first collectorrotat'ably mounted on said shaft to be positioned, a lost motion connection between said first adjusting member and said first collector, a second collector operatively connected to said second adjusting member, selector means operatively connected to said rotary adjusting members, a motor, a main drive shaft operatively connected to said motor provided with transmission means for said rotary adjusting members, the transmission means between said main drive shaft and said first rotary adjusting member having a greater speed reduction than the transmission means between said main drive shaft and the second rotary adjusting member, said first rotary adjusting member during positioning of said shaft determines the end of the lost motion sector within which the selected position is situa'ted, and means including said motor for rotating both said first and second rotary adjusting members in the opposite direction to the original direction of rotation to position said shaft in the selected position within the sector selected by said first rotary adjusting member starting from the end of the sector selected by saidfirst rotary adjusting member.

'2. A shaft positioning mechanism as claimed in claim 1 wherein all the sectors traversed by said rotary adjusting members have t' e same angular value and whole parts of '360. V r

'3. A shaft positioning mechanism as claimed in claim 1 wherein said selector means includes a collector and a coupling between said second rotary adjusting member and said collector permitting the free movement of said second rotary adjusting member relative to said collector.

'4. A shaft positioning mechanism as claimed in claim 3 wherein the free movement of said second rotary adjust- 'ingmember relative to said collector is possible through an angle having at least the same value as the angular valueof said sector.

'5. A shaft positioning mechanism for positioning a shaft in a plurality of preset positions comprising first and second rotary adjusting members, said first adjusting memberbeing rigidly connected to said shaft to be posi- 'tioned, a first collector rotatably mounted on said shaft to be positioned, a 10st motion connection between said "first adjusting'member and said first collector, a second collector 'operatively connected to said second adjusting member, selector means operatively connected to said rotary adjusting members, a motor, a main drive shaft operatively connected to said motor with transmission means for said rotary adjusting members, the transmission means between said main drive shaft and said first rotary adjusting member having a greater speed reduction than the transmission means between said main drive rotary adjustingmember during positioning of said shaft determines the end of the lost motion sector within which the, selected position is situated, and means including said motor for rotating both said first and second rotary adjusting member in the opposite direction to the original direction of rotation to position said shaft in the selected position'within' the'sector selected bysaid first rotary adjusting member starting from the end of the sector selected by saidfirst rotary adjusting member, said second rotary adjusting member being constituted of two parts, one part being a ratchet wheel and having a collector rigidly connected thereto and the other part being an auxiliary member driven by said driving shaft, a coupling provided between said two parts permitting free rotation of said .auxiliary'member with respect to said ratchet wheel in one direction of rotation whereas in the other direction of rotation the auxiliary member may per'form a "rotation of at most 360 with respect to said ratchet wheel.

6. A shaft positioning mechanism as claimed in claim 5 further comprising a pawl, means electrically operating said pawl relative to said ratchet Wheel, the position of said ratchet 'wheelbeing determined by said collector rigidly connected thereto.

7. Ashaft positioning mechanism as claimed in claim 5 wherein said ratchet wheel and collector are adapted to rotate about said drive shaft, and a friction coupling is "provided between "said two parts.

' 8. A shaft positioning mechanism asclaimed'in claim 5 further comprising asecond drive shaft operatively connected to said main-drive shaft driving said ratchet wheel with its collector.

9. A shaft positioning mechanism "for positioning a shaft in a plurality of preset positions comprising first and second rotary adjusting members, said first adjusting member being rigidly connected to said shaft to be positioned, a first collector rotatably mounted on said shaft to be positioned, a lost motion connection-between said first "adjusting member and said first collector, a

second collector operatively connected to said second adjusting member, selector means operatively connected 1 to said rotary adjusting members, amotor, a main drive shaft operatively connected to said motor with transmission 'means for said rotary adjusting members, the

transmission means between 'saidmain "drive shaft and said first rotary adjusting member having a greater speed reduction thanthe transmission means-between said drive shaft and the 'secondrotary adjusting'memben-said first rotary adjustingmernber during positioning of said shaft determines the end of a sector of the total angle of rotation within which the selected position is situated, and n'tcans including said motorfor rotatingboth said first and second rotary adjusting members in the opposite direction to the original direction of rotationto position said shaft in the selected position within the sector selected by said first rotary adjusting member starting 7 from the end :of the sector selected by said first rotary adjusting member, and said second rotary adjusting memher being operatively connected to said main drive shaft and driving said shaft to be positioned.

1.0. A shaft positioning mechanism .as claimed in claim 1 wherein said shaft to be positioned is directly coupled with's ai'd main drive shaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,094,475 French fDec. s, .1954 

